Bulk–edge correspondence and trapping at a non-Hermitian topological interface

In Hermitian systems, according to the bulk–edge correspondence,
interfacing two topological optical media with
different bulk topological numbers implies the existence of
edge states, which can trap light at the interface. However,
such a general scenario can be violated when dealing with
non-Hermitian systems. Here we show that interfacing two
semi-infinite Hatano–Nelson chains with different bulk topological
numbers can result in the existence of infinitely many
edge (interface) states; however, light waves cannot be rather
generally trapped at the interface